The use of various types of sensors to evaluate one or more physiological parameters of a patient is well known. For example, optical pulse oximetry sensors measure the level of oxygen saturation (SpO2) in a patient's blood. In one such sensor, a light-emitting diode (LED) transmits optical radiation of several different wavelengths, e.g., visible and infrared, through blood and tissue of a predetermined portion of a patient's body; typically, the wrist or finger. A photodetector detects the light (human-visible or other wavelengths) after it passes through the body. Different wavelengths of light are absorbed differently based on blood oxygen content, so detecting the optical attenuation at each wavelength permits determining oxygen saturation. In another example, electrocardiogram (ECG or EKG) electrodes are generally planar electrodes connected via wires to an ECG unit that measures the voltage across different pairs of the electrodes to monitor the patient's heart. It is generally required that physiologic sensors be correctly placed with respect to a specific body part to be measured. For example, a pulse oximetry sensor should be placed so that the optical path from the transmitter to the detector intersects a blood vessel. Likewise, an ECG sensor should be placed on a part of the body that provides effective electrical contact across the skin (e.g., not on top of significant amounts of hair). It is also generally required that the sensor effectively contact the patient's body to make accurate measurements.
Many types of sensors are rigid or are fabricated at least in part using rigid substrates. However, specific areas of the human body change shape while moving, e.g., as muscles alternately contract and relax. In order to maintain contact of a rigid sensor to a flexible body, some prior schemes describe bands carrying the sensors, or sensors embedded in clothing. However, these schemes are limited in the accuracy with which they can maintain position. Other schemes apply pressure to a body part, e.g., by pressurizing the inside of a ring on a patient's finger, to retain the sensor in position with respect to that body part. However, these schemes can require expensive supports for the sensors and can cause increased patient discomfort. Alternative schemes permit the sensor to move with respect to the body part, then compensate for that motion.
Even if the sensor is retained in place with respect to the body, or motions are compensated for, it is still desirable for the sensor to effectively contact the body. For example, a skin conductance sensor has two electrodes that contact the skin to measure the resistance or voltage between the two electrodes. Since these electrodes are directly in contact with the skin in conventional systems, the electrodes can become contaminated with, e.g., oil, water, or salt over time. This contamination can reduce the accuracy of the sensor. It is known to clean sensors periodically. However, every cleaning cycle can cause water damage or other types of wear to the sensor or its electrodes. Moreover, recalibration of the sensor may be required after cleaning to correct for this wear.